It is known that titanium boride is a very tough material which is resistant to oxidation and is a good electrical conductor; it may therefore be advantageously used as the material for electrodes in the sphere of aluminum production by electrolysis (Hall-Heroult methods and others). When it is pure and compact it resists thermal shocks and corrosion by molten aluminum and cryolite. In industry the parts to be used as electrolyzers are obtained from TiB.sub.2 powder, either by hot sintering under pressure when the powder is very pure, or by normal sintering when the oxygen content (TiO.sub.2 or B.sub.2 O.sub.3) in the starting powder is high.
As the quality of the materials obtained in the second case is not sufficient for the intended use, since the presence of oxides in the sintered material causes a very marked reduction in its resistance to corrosion and thermal shock, only the pressure sintering method enables parts to be produced which meet the above-mentioned requirements. However, pure TiB.sub.2 sintered parts, obtained by high pressure thermal sintering of titanium boride powder, are expensive and difficult to obtain owing to the technical problems connected with the simultaneous application of high temperatures and high pressures.
These difficulties have been overcome by using densifying additives during pressureless thermal sintering, which enable high density compact forms to be produced. Metal silicides of groups 4a to 6a of the periodic table (U.S. Pat. No. 4,017,426), nickel phosphide and a component selected from Cr, Mo, Nb, Ta, Re, Al and their borides (U.S. Pat. No. 4,246,027), tungsten, titanium and boron carbides (U.S. Pat. No. 4,108,670) and boron nitride (U.S. Pat. No. 4,097,567) may be cited as additives of this type. However, the sintering of TiB.sub.2 powders containing such additives produces forms in which these additives remain included, which is undesirable for the following reasons: contamination of the molten aluminium and pollution of the latter by these impurities, undesirable slow restructuring of the electrode material, low resistance to thermal shocks. During the course of the electrolysis of aluminium ores the presence of impurities in the TiB.sub.2 leads to the formation of a large-grained structure which is more fragile, less resistant to corrosion and to the precipitation of Ti.sub.2 AlN and Ti.sub.2 AlC type phases, by the slow migration of the impurities when carbides or nitrides are used as additives.